Ultimately, as good as the first nine seasons were, given the ratio of bad seasons to good at this point, I don't think you can actually call 'the Simpsons' a good show, only a long running one. Trying to define the entire run by the early years is akin to saying that 'Lost in Space' wasn't camp merely because the first few episodes were darker in tone than all the ones that came after.

The problem is that you're underselling just how good the first nine seasons were. The Simpsons wasn't just a good comedy back then, it was the definitive comedy series of the 1990s, and most people would list those first nine years on their own as one of the best television series of all time. There's a reason why the latter fifteen seasons were made, and it has everything to do with those first nine. Viewing the show as the average of all it parts means that you're missing that hugely important caveat.

I understand your argument. At his point, however, those brilliant nine seasons are way less than one half of the shows run. It's like trying to argue 'Rocky 1' makes the entire film series Oscar-worthy.